1. Field of the Invention
The present invention relates to a content distribution system, a method for distributing content and a program thereof, and more particularly it relates to a content distribution system, a method for distributing content for performing a simultaneous distribution of same multimedia content to a plurality of mobile communication terminals, that is, performing one-to-many distribution (herein referred to as “multicasting”) of content.
2. Related Art
In the past, in the case of distributing of content such as characters, music, images, or computer programs and the like to users terminals (mobile communication terminals such as cellular telephones), multicasting of the content was performed using a multicasting channel.
In a system for multicasting content using a multicasting channel, it is in principle possible to use one and the same wireless resource to distribute the same content to all user terminals existing within the area reached by the signal on the channel, and in this system, it is possible to provide a high efficiency with respect to wireless resources, compared with the case of a system in which each individual wireless resource is distributed to each user terminal individually.
However, the area reached by the wireless signal has a service area that is limited by the wireless environment, which changes in accordance with, for example, the shape of the coverage area, the existence or absence of structures, or temporary movement of radio wave blocking objects. In such a situation, it is difficult to guarantee continuous and/or stabled distribution of content to all users. Given this, it is possible to envision, for the purpose of performing content distribution more reliably, an increase in the transmitter output power at a base station, or the allocation of different wireless channels for each user terminal.
In the case in which the transmission power is increased, however, because of an increase in interference power relative to other users in the same or a neighboring area, there results a decrease in the number of user terminals that can be accommodated. In the case of allocating different wireless channels for each user terminal, because as many wireless channels are required as there are user terminals, there is a drop in the efficiency of usage of wireless resources, compared with the above-noted system using a multicasting channel.
In order to more reliably distribute content, it is possible to envision a system in which a user terminal that was not able to receive content requests the network to resend the content via a multicasting channel. In this case, however, the distribution of new content to user terminals that received normally is hindered, this being undesirable from the standpoint of maintaining the real-time distribution of the content.
With respect to content to be distributed to the users, there is content that is charged a fee and content that is provided for a fee, and in the case of free content even if reception was temporarily or for a long time not possible no problem would occur regarding a contractual relationship, but for paid content if it is not possible to fulfill the contractual condition of distributing content, a contractual problem would occur. Therefore, particularly in the case of paid-for content, it is important to resend content in the case in which a user terminal fails to receive the content.
However, the sending of not only yet-to-be distributed content but already-distributed content in response to a request from a user terminal occupies a wireless channel for a prescribed time, thereby resulting in decreasing of the number of user terminals that can be accommodated, it is desirable that re-distributing be done selectively, to only user terminals which requests such re-distributing.
Additionally, the re-distributing of content should only be done to user terminals properly registered for the distribution of the content, and it is desirable that even should there be a request from an improper user terminal not registered for distribution, there is no re-distributing to the improper user terminal.
Accordingly, it is an object of the present invention to provide content distribution system, a method for distributing content, a radio network controller, and a program, which can achieve highly reliable content distribution with effective usage of wireless resources.